The amount of time guests stay at sea played a major role in determining the ships' differences, said Joe Lanzisero, senior vice president for creative at Walt Disney Imagineering. The Fantasy offers seven-night cruises to the western and eastern Caribbean, while three- and four-night cruises are available on the Dream.

Fantasy's amenities and entertainment reflect that more leisurely pace. There are small pools in two new locations, including the adults-only Satellite Falls.

The corresponding areas of the Dream are dry and dominated by deck chairs. And a bar on the Dream's pool deck is an interactive water-play area called AquaLab on the Fantasy.

"Instead of having everybody in that central pool area waiting to get on the AquaDuck [water coaster], now you've got a couple of destinations that they can go," said Lou Mongello, a Disney expert, author, host and operator of WDWRadio.com.

Adjustments also extend to the stage shows, creative director David Duffy said.

Passengers are "in a different mind-set after a day at sea. They walk into the theater in a slightly different place than after a port day," Duffy said.

A relaxed mood helps audiences follow a more-involved, single-subject story, he said. On the Fantasy, passengers can see "Aladdin," a version of the stage show at Disney's California Adventure theme park. The shows on the Dream are fast-paced revues, a sort of "Disney's greatest hits" format.

Changes also are found in the Fantasy's nightclub district, known as Europa.

The Tube, the Fantasy's dance club, will throw theme parties saluting English music from the Beatles to Adele plus live entertainment. Variety helps boost the club's repeatability factor, Duffy said.

"We have singers that will be a part of the event in the nightclub, which is something new for us," he said. "With the Dream, the [club] spaces are somewhat contemporary but not necessarily themed."

Passengers will notice changes in decor as they enter the Fantasy's three-deck atrium, with its peacock-inspired features in the carpeting and chandelier. The Dream's style is sleek art deco, but the Fantasy is the more decorative art nouveau, Lanzisero said.

"I think guests will find the look and feel of the Fantasy a bit more theatrical, different. Whereas the Dream, the art deco is a little more refined and elegant," he said.

The differences should appeal to Disney devotees, Mongello said.

"I think for some people, there is definitely something exciting about saying that you were on all four ships," he said. The first two vessels, Disney Magic and Disney Wonder, debuted in the late 1990s.

Fantasy's journey

The Fantasy will be christened in New York on Thursday. On March 6, it will arrive at its Port Canaveral base, also home of the Dream. Its maiden voyage will be March 31.

The two newest Disney Cruise Line ships were manufactured by the Meyer Werft shipyard in Papenburg, Germany. Both are 1,115 feet long with room for 4,000 passengers. Although the specifications are identical for the ships, which cost $900 million apiece, Disney's plan was to make their sailing experiences different.

Although the Dream launched 13 months ago, the plans for the Fantasy were too far along to make big changes based on passenger feedback, Lanzisero said.

"When you're doing a project the size of these ships, there are literally hundreds of thousands, maybe millions of choices that we make about everything from where you put a knob to the kind of material you use," he said. "We made little subtle changes everywhere, most of which guests will never see."

Disney isn't alone in building ships in series.

Royal Caribbean International has two identical ships under construction and Carnival Cruise Line's Dream, based in Port Canaveral, was the first of three ships in a set, said Stewart Chiron, a Miami-based cruise expert known as "The Cruise Guy."

Carnival Corp. even has one class of ship with 18 versions around the world, he said.

"It just saves an enormous amount of money, not having to design something from the ground up," Chiron said. "It provides continuity, consistency, familiarity to their passengers."